Why do people(you, in this case, but this is a very common fallacy) assume that advocating for one thing(idleness) is implicitly advocating against its opposite(work)? We can do both, just not simultaneously.
Because the article's title is "The Importance of Being Idle" not The Importance of doing something that you enjoy"? It's all-too-easy to enjoy being idle, but ultimately it's also a bit mindless, and this deprives us of deeper forms of enjoyment and engagement.
it seems like you are interpreting this as an argument for "not doing work" - but it's not the case. It is more so saying that rest is important too. You ever have the experience that you are bashing your head against something, take a break to stop working on it, and come back refreshed and solve it quickly? Just because something is important, doesn't mean you should do that thing, single-mindedly, at the expense of other things.